Rate

Any

Regularity

Irregular pattern, but regular R-R

P waves

Upright and uniform

PRI

No relationship between P and QRS

QRS

May be narrow or wide

Rate

60-100

Regularity

Irregular

P waves

Morphology changes

PRI

Changes

QRS

0.08-0.12

Rate

Any

Regularity

Regularly Irregular

P waves

Upright and uniform

PRI

Gradually lengthening until dropped

QRS

0.08-0.12